How Exactly Does Bleach Manage To Kill Bacteria?

A new study suggests that the antimicrobial effects of common bleach are largely based on its ability to cause aggregation of essential bacterial proteins.

Researchers at the University of Michigan (Ann Arbor, MI, USA) have discovered how Hypochlorous acid (HOCl), the active ingredient in household bleach, manages to be such an effective antimicrobial agent. The researchers had been studying a bacterial protein called heat shock protein 33 (Hsp33), which is a kind of molecular chaperon that becomes active when cells are in distress. In this case, the source of the distress was HOCl. When they exposed the bacteria to the bleach, the heat shock protein became active by the reversible oxidative unfolding of its C-terminal redox switch domain, turning the inactive Hsp33 into a highly active chaperone holdase, which protects essential Escherichia coli proteins by forming clumps in an attempt to protect other proteins in the bacteria from losing their chemical structure. The researchers explained that the human immune system also produces HOCl in response to infection, but that the substance kills not only the bacterial invaders but human cells as well, which may explain how tissue is destroyed in chronic inflammation, due to the targeting of thermolabile proteins, thereby causing irreversible aggregation. The study was published in the November 14, 2008, issue of the journal Cell.

"Hypochlorous acid is an important part of host defense,” said lead author Associate Professor Ursula Jakob, Ph.D., and colleagues of the department of molecular, cellular, and developmental biology. "It's not just something we use on our countertops.”

Hypochlorous acid is a weak acid that bonds when chlorine dissolves in water. In the body, HOCl is generated in activated neutrophils by peroxidation of chloride ions.

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